How long is a pause compared to a beat? Or is it just preference?
— Kurt Yaeger
San Francisco
They mean the same thing, though I almost always use beat.
That said, it’s very easy to overuse them. Most times, dialogue reads fine without any special indicators, so save them for when they’re truly needed.
You should know that some screenwriters (and some readers) really despise the term “beat.” If you fall into that camp, it’s not hard to avoid using it. Scripting an action — “(cracking his knuckles)” — is handy, but almost anything in a parenthetical would do the trick.